1. Field of the Invention
This invention pertains generally to the field of oscillators and frequency recognition devices, and more particularly to such devices having multiple modes or frequencies of oscillation.
2. Description of the Prior Art
Standing waves on transmission lines are a well known phenomena, with the number of the standing waves present, and the frequency of the standing wave being related to the length of the transmission line and the inductance and capacitance of the line. A transmission line is, of course, a distributed parameter system, the dynamics of which are described by partial differential equations. However, such transmission lines have been approximated by a ladder network consisting of a large number of small, serially connected inductors to simulate the self inductance of the transmission line, with small capacitors connected from the connections between the inductors to ground to simulate the distributed capacitance between the transmission line and ground. Such networks have been denoted LC ladder oscillators because they have series inductance and shunt capacitance. In theory, a distributed parameter oscillatory system has an unlimited number of degrees of freedom, or standing wave frequencies which it can support, while the discrete component analog can support only a finite number of frequencies.
Standing waves on one and two-dimensional LC networks of capacitors and inductors with distributed non-linearities have been analyzed by several investigators. It has been determined that several modes of oscillation can be excited simultaneously and asynchronously on a two-dimensional array composed of inductors and capacitors interconnected to form a grid, extending in at least two dimensions. In the one-dimensional LC ladder network such oscillations were determined to be unstable, and only a single mode of oscillation was observed. An oscillator which has several stable states of oscillation may be denoted a multistate oscillator, and an oscillator which is capable of oscillating in either individual oscillation modes or combinations of the oscillation modes may be denoted a multimode oscillator. Such oscillators may be passive, in that they consist only of passive linear elements such as capacitors and inductors, or they may be active and are capable of sustaining autonomous oscillations. It has been found that active LC ladder oscillators will support only one stable mode of autonomous oscillation, at the fundamental or lowest mode frequency of the oscillator.